Determining the available amount of RAM on an iOS device

Question

You've likely seen the many "System Info" apps out there which display things like remaining battery life, and even system info like memory, etc.

In a similar manner, is there any way to retrieve the current amount of available RAM from my app so that I can make better decisions on when it's best to dump or keep certain views to avoid memory warnings?

Solution 1

#import <mach/mach.h>
#import <mach/mach_host.h>

void print_free_memory ()
{
    mach_port_t host_port;
    mach_msg_type_number_t host_size;
    vm_size_t pagesize;

    host_port = mach_host_self();
    host_size = sizeof(vm_statistics_data_t) / sizeof(integer_t);
    host_page_size(host_port, &pagesize);        

    vm_statistics_data_t vm_stat;

    if (host_statistics(host_port, HOST_VM_INFO, (host_info_t)&vm_stat, &host_size) != KERN_SUCCESS) {
        NSLog(@"Failed to fetch vm statistics");
    }

    /* Stats in bytes */ 
    natural_t mem_used = (vm_stat.active_count +
                          vm_stat.inactive_count +
                          vm_stat.wire_count) * pagesize;
    natural_t mem_free = vm_stat.free_count * pagesize;
    natural_t mem_total = mem_used + mem_free;
    NSLog(@"used: %u free: %u total: %u", mem_used, mem_free, mem_total);
}

Please note that this call does not account for memory that is being used by the gpu. If you are seeing a size that is smaller than expected system ram. It is more than likely allocated graphics memory.

Solution 2

This works in Swift 4.

The really important difference here is: It casts to Int64 before multiplying, because otherwise you get quickly overflows, especially if you run it in a simulator where it uses the PC Memory.

var pagesize: vm_size_t = 0

let host_port: mach_port_t = mach_host_self()
var host_size: mach_msg_type_number_t = mach_msg_type_number_t(MemoryLayout<vm_statistics_data_t>.stride / MemoryLayout<integer_t>.stride)
host_page_size(host_port, &pagesize)

var vm_stat: vm_statistics = vm_statistics_data_t()
withUnsafeMutablePointer(to: &vm_stat) { (vmStatPointer) -> Void in
    vmStatPointer.withMemoryRebound(to: integer_t.self, capacity: Int(host_size)) {
        if (host_statistics(host_port, HOST_VM_INFO, $0, &host_size) != KERN_SUCCESS) {
            NSLog("Error: Failed to fetch vm statistics")
        }
    }
}

/* Stats in bytes */
let mem_used: Int64 = Int64(vm_stat.active_count +
        vm_stat.inactive_count +
        vm_stat.wire_count) * Int64(pagesize)
let mem_free: Int64 = Int64(vm_stat.free_count) * Int64(pagesize)

Solution 3

You can check the available RAM Memory in an iOS devices

    #import mach\mach.h
    #import mach\mach_host.h

     static natural_t get_free_memory(void)  
     {  
       mach_port_t host_port;  
       mach_msg_type_number_t host_size;  
       vm_size_t pagesize;  
       host_port = mach_host_self();  
       host_size = sizeof(vm_statistics_data_t) / sizeof(integer_t);  
       host_page_size(host_port, &pagesize);  
       vm_statistics_data_t vm_stat;  
       if (host_statistics(host_port, HOST_VM_INFO, (host_info_t)&vm_stat, &host_size) != KERN_SUCCESS)  
       {  
         NSLog(@"Failed to fetch vm statistics");  
         return 0;  
       }  
       /* Stats in bytes */  
       natural_t mem_free = vm_stat.free_count * pagesize;  
       return mem_free;  
     }  

Comments

[David H]

I'm shocked that I'm the first person to give you a point on this code. Its working great on my iPhone and is a huge help to me! I wish I could give you 10 points!!!

[David H]

I did find one other command you can add to the above, to get task stats: struct task_basic_info info; if(dump_memory_usage(&info)) { fm.resident_size = (size_t)info.resident_size; fm.virtual_size = (size_t)info.virtual_size; }

[Steve]

If you want to true TOTAL RAM the device has, just use [NSProcessInfo processInfo].physicalMemory.

[Nico]

@Steve, Provides the amount of physical memory on the computer. - (unsigned long long)physicalMemory How does this tell you how much memory your application is using?

[Steve]

@Nico, it doesn't. It tells the total system RAM. I recommend this instead of mem_total/mem_free, not instead of mem_used. This is because mem_total/mem_free depend on how much RAM is being used by other apps to, and so it's a completely unreliable indicator for pretty much anything.

[Nico]

@Steve The nice part about mem_total is shrinks graphics memory is allocated

[Nico]

There are no private apis called here so yes.

[Petr]

Do you know, this takes in account memory used by GPU, or no?

[alexandrmoroz]

Has anyone check that this code works correct at 64bit devices?

[Mathias Van Houtte]

Hello I tried your example but I have very different values for mem_used. When I convert it to MB, it gives me 120MB while in XCode, it gives me 30MB. Any idea why?

[ingconti]

why backslashes in mach\mach.h ?

[Thomas Elliot]

I believe the total memory calculation is inaccurate. Cross-reference it with [NSProcessInfo processInfo].physicalMemory and you'll see the latter is more closely aligned with the device's marketed memory spec.

[Kleomenis Katevas]

Thanks for this. Just a comment, I think the Int64 should be UInt64.

[Jan]

@Minos I disagree. Remember that 2^63 is already 9,223,372,036,854,775,808 and Int64 has as signed integer the advantage that some subtractions won't produce exceptions when going below 0.

[Srishti Roy]

@Nico which one is relevant NSProcessInfo processInfo].physicalMemory ,this one gives in bytes?

[Jeba Moses]

YES. NSProcessInfo processInfo].physicalMemory returns you total RAM size in bytes.

[Ky -]

Why MemoryLayout.stride instead of MemoryLayout.size?